This application is based on Japanese Patent Application No. 2002-56492 filed on Mar. 1, 2002 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection quantity controller for an internal combustion engine. More specifically, the present invention relates to a pilot injection quantity controller for an internal combustion engine, capable of driving a fuel injector a plurality of times while the engine is in a compression stroke to inject a small quantity of fuel at least once for pilot injection before main injection.
2. Description of Related Art
A conventional common rail type fuel injection system injects a high-pressure fuel stored in a common rail under pressure into the cylinders of a multi-cylinder diesel engine. This common rail type fuel injection system performs pilot injection several times prior to main injection that makes the engine produce torque to reduce combustion noise and engine vibrations by stabilizing combustion from the start of main injection and to improve the quality of the exhaust gas.
Usually, the variation of an actual injection quantity in an injection command pulse time (TQ pulse width) for which the fuel injector injects fuel is corrected by individually adjusting the fuel injectors of the cylinders. Since the pilot injection quantity is as small as 5 mm3/st, the pilot injection cannot achieve its purpose satisfactorily due to the variation of the actual injection quantity in the injection command pulse time, and the failure of pilot injection or injection of an excessive quantity of the fuel due to the deterioration of the ability of the fuel injector resulting from the secular change of injection quantity. The actual injection quantity injected by the fuel injector in the injection command pulse time tends to vary in a wide range when the injection pressure is high. Thus, it is very difficult to guarantee the performance of the fuel injector when the injection quantity is as small as on the order of 1 mm3/st.
An inter-cylinder engine speed variation injection quantity correcting technique (FCCB) has been proposed to solve the foregoing problems. Application of this correcting technique is limited only to the correction of fuel injection pressure during idling, and this correcting technique cannot achieve correct correction of fuel injection pressure while the vehicle is running and when fuel injection pressure is high.
A method of proportionally distributing an injection quantity correction to two injection cycles, i.e., a pilot injection cycle and a main injection cycle is proposed in JP-A 2-23252. Application of this method, similarly to that of the foregoing known technique, is limited to the correction of fuel injection pressure during idling, and this method is unable to achieve accurate correction. Since this method distributes an injection quantity correction to the pilot injection cycle and the main injection cycle in proportion to the ratio of a pilot injection quantity to a total injection quantity and the ratio of a main injection quantity to the total injection, quantity, respectively, the method determines an estimated fuel injection quantity correction and is unable to quantitatively determine the divergence of an injection quantity relative to an injection command pulse time for the injector.
It is an object of the present invention to provide an injection quantity controller for an internal combustion engine, capable of quantitatively determining an actual injection quantity to be injected in an injection command pulse time by an injector.
According to a first aspect of the present invention, an injection quantity controller for an internal combustion engine calculates a learning control mode injection quantity according to the operating condition of the engine when learning executing conditions dependent on a predetermined operating condition of the engine or operating conditions for the engine are valid, substantially uniformly divides the learning control mode injection quantity by n, achieves inter-cylinder engine speed variation correction for individually correcting injection quantities for cylinders to smooth engine speed variation in each cylinder by measuring engine speed variation in each cylinder while n split injection cycles are performed, and comparing the engine speed variations in all the cylinders with a mean value, and achieves mean engine speed correction by measuring the mean engine speed while the n injection cycles are performed, and uniformly correcting the injection quantities for all the cylinders so that the mean engine speed is maintained at the desired engine speed for mean engine speed correction.
Furthermore, the injection quantity controller calculates, for each cylinder, a first injection quantity correction corresponding to the deviation of a measured engine speed variation in each cylinder from a mean engine speed variation of engine speed variations in all the cylinders, calculates a uniform second injection quantity correction for all the cylinders necessary to maintain the mean engine speed at the desired engine speed, and adds up a value obtained by dividing the first injection quantity correction for each cylinder by n and a value obtained by dividing the uniform second injection quantity correction for all the cylinders by n. Thus, the difference between an actual injection quantity and an injection quantity to be injected by the injector in the command injection pulse time, and the deterioration of the performance of each injector due to the secular change of injection quantity can be quantitatively determined for each cylinder. The relation between an ideal command injection pulse time and an injection quantity can be determined by adding up and storing the difference and the learned value learned by the preceding learning cycle as a learned fuel injection quantity for each cylinder.
The present invention may be implemented in the following manner.
The first and the second correction calculating means calculate the first injection quantity correction for each cylinder and the uniform second injection quantity correction for all the cylinders for a plurality of different fuel injection pressure levels, and the learned value storage means updates and stores learned values for the plurality of different fuel injection pressure levels. Thus, the difference between an injection quantity to be injected in the injection command pulse time by the injector and an actual injection quantity can be quantitatively determined in a state where the engine is in operation even at a high fuel injection pressure and at a very small injection quantity, which is difficult to guarantee even by the single injector.
The learned values stored by the learned value storage means for fuel injection pressure levels other than the plurality of different fuel injection pressure levels are determined by interpolation. Thus, the learned values stored by the learned value storage means for the entire working range of fuel injection pressure in an actual vehicle including fuel injection pressures in the learning control mode can be used as corrections to be reflected in calculating the fuel injection quantity for each cylinder. Consequently, an ideal correlation between command injection pulse time and fuel injection quantity can be maintained.
The learned value indicates a deviation of an actual injection quantity from an injection quantity to be injected in the command injection pulse time for each fuel injection pressure and each cylinder of the engine.
It is known that a temporary learned value including a change, caused by load on the engine, of an engine demand injection quantity is abnormally greater than other temporary learned values. Therefore, the injection quantity controller is provided with the temporary learned value storage means capable of dividing the learned control mode injection quantity into substantially equal n injection quantities, of calculating a learned value of, for example, injection quantity by adding up the first injection quantity correction for each cylinder or a value obtained by dividing the first correction by n, and the uniform second injection quantity correction or a value obtained by dividing the second correction by n while the inter-cylinder engine speed variation correction and the mean engine speed correction are being carried out, and of repeating the learning control operation a plurality of times to update and store the learned values calculated by repeating the learning control operation a plurality of times. The minimum value for each fuel injection pressure and each cylinder among the plurality of updated and stored learned values is used as the final learned value to determine whether or not the temporary learned value is normal. Since excessive correction of fuel injection quantity resulting from false learning (false correction) or excessive learning (excessive correction) can be prevented, the increase of combustion noise and vibrations of the engine, and the deterioration of emissions can be avoided. Thus, the minimum temporary learned value among the temporary learned values obtained by the plurality of learning control operations, i.e., a proper temporary learned value, can be reflected as the final learned value (correction) in the fuel injection quantity.
The calculation of learned value for every one of learned values of the plurality of different fuel injection pressure levels and for selecting the minimum value among the plurality of temporary learned valves as the final learned value to improve the learning accuracy (correcting accuracy) corresponding to the deterioration of the performance of the injector due to the deviation of the actual injection quantity from the injection quantity to be injected in the command injection pulse time increases combustion noise due to high-pressure injection. Therefore, it is desirable to calculate the learned value or the temporary learned value at a predetermined learned value calculating frequency or a predetermined correcting frequency. However, when the learned value is calculated at the predetermined learned value calculating frequency or the predetermined correcting frequency, a state in which an injection quantity of fuel different from a proper injection quantity is injected is continued until the next learned value or temporary learned value is calculated and hence the performance of the engine is deteriorated if an unexpected sudden change of injection quantity occurs or when the calculation of a learned value or a temporary learned value is executed without detecting a state in which a load, such as an electrical load, is applied to the engine.
The accuracy of decision of false learning can be improved by providing a command to perform the inter-cylinder engine speed variation correction and the mean engine speed correction again from the beginning when the uniform second injection quantity correction for all the cylinders or the second correction is smaller than a predetermined value under a condition other than the learning executing conditions, and to perform a learning control operation that updates and stores the calculated learned value, a fuel injection quantity corresponding to the desired fuel injection quantity can be determined for a period preceding the calculation of the next learned value or temporary learned value by executing learning again after false learning, and the deterioration of the performance of the engine can be prevented. When a state where a load, such as an electrical load, is applied to the engine can be detected during relearning control, time necessary for calculating the final learned value can be greatly curtailed by using a temporary learned value calculated by a single learning control cycle as the final learned value, as compared with the learning control that uses the minimum value among the plurality of temporary learned values calculated by a plurality of learning control cycles as the final learned value.
A command is provided not to store a learned value obtained by the present learning control cycle and to start the learning control cycle from the beginning or to inhibit or suspend the learning control operation when the difference between a learned value obtained by the preceding learning control cycle and that obtained by the present learning control cycle is outside a predetermined range or when an integrated learned value is greater than a predetermined value. Thus, false learning or excessive learning can be prevented.
A command is provided to inhibit or suspend the learning control operation upon the increase of the uniform second injection quantity correction for all the cylinders or the second correction from the start of the learning control operation by a value greater than a predetermined value. Thus, false learning or excessive learning can be prevented.
It is possible that false correction or excessive correction occurs when a learned value is used due to the effect of fuel injection quantity, fuel injection pressure and engine speed when a learned value is reflected in a region other than that for learning control mode. Excessive correction of fuel injection quantity caused by false correction or excessive correction can be prevented by using a value obtained by tempering the learned value or the temporary learned value with a correction coefficient serving as a measure of the characteristics of a fuel injection system as a learned correction. Thus, the increase of combustion noise and vibrations of the engine and the deterioration of emissions can be prevented, and a proper learned correction can be reflected as a correction in fuel injection quantity.
When an idling injection quantity (learning control mode injection quantity) corresponding to a predetermined operating condition of the engine or to idling fuel consumption includes an increment of engine demand injection quantity due to loading of the engine, false learning occurs and a learned value including the increment of engine demand injection quantity in addition to an amount of scatter of injection quantities and a secular change of injection quantity is calculated. A difference between the injection quantity and the idling fuel consumption can be distinguished and the effect of the change of the engine demand injection quantity can be removed from the amount of scatter of injection quantities and the secular change of injection quantity, when the learned value or the false learned value of the idling injection quantity (learning control mode injection quantity) corresponding to the idling fuel consumption is determined by subtracting a change in the set engine demand injection quantity corresponding to the variation of load on the engine from the sum of the first injection quantity correction or the first correction, and the second injection quantity correction or the second correction or adding the same to the sum of the first injection quantity correction or the first correction, and the second injection quantity correction. Thus, excessive correction of fuel injection quantity resulting from false learning (false correction) or excessive learning (excessive correction) can be prevented. Consequently, the increase of combustion noise and vibrations of the engine, and the deterioration of emissions can be prevented, and a proper learned injection quantity can be reflected as a correction in the fuel injection quantity.
When a learning control operation is performed to divide the learning control mode injection quantity substantially uniformly for n injection cycles, to calculate, for example, a learned injection quantity by adding up a value obtained by dividing the first injection quantity correction or the first correction for each cylinder by n and a value obtained by dividing the uniform second injection quantity correction for all the cylinders or the second correction by n while inter-cylinder engine speed variation correction and mean engine speed correction are being performed, and to update and store the calculated learned injection quantity, the learning control operation continues indefinitely and the deterioration of the performance (function) of the injector due to the variation of the injection quantity and the secular change of injection quantity cannot be corrected if the learning executing conditions are invalidated by operations, such as depression of the accelerator pedal and closing of the switch of the air conditioner, and learning control operation is suspended frequently.
Time necessary for completing a learning control operation can be curtailed by starting the succeeding learning control operation after the learning conditions have become valid from a learning state where the preceding learning control operation was suspended due to the invalidity of the learning executing conditions. Thus, the learning control operation can be surely completed even if the learning control operation is suspended frequently. Even when a learning control operation for calculating an injection quantity, as a temporary learned value, by adding up a value obtained by dividing the first correction or the first correction for each cylinder by n and a value obtained by dividing the uniform second correction or the second correction for all the cylinders by n, and updating and storing the calculated injection quantity is executed a plurality of times, the calculation of the next temporary learned value can be started without calculating the first temporary learned value by starting the succeeding learning control operation after the learning conditions have become valid from a learning state where the preceding learning control operation was suspended.
The learning executing conditions are valid under a condition where an idling fuel consumption state and false learning is detected or where the frequency of an ignition switch opening operation, the distance traveled by a vehicle, the operating time of the engine or the secular reduction of injection quantity resulting from the deterioration of the performance and function of the injector due to the secular change of injection quantity meets predetermined conditions and is invalid under conditions other than the foregoing condition. Use of input information about the change of load on the engine, such as power for driving engine accessories and electrical loads, the setting of the select lever in the neutral range or the parking range, or a condition where the clutch pedal is depressed by the driver in combination will enable the further effective detection of a state where the engine is operating at an idling fuel consumption.
If an injector has, for example, an injection quantity changing characteristic such that the injection quantity does not change at a fixed time rate, the secular change of injection quantity cannot be corrected by a learned correction if the frequency of calculation of learned value or the frequency of correction is excessively low, and the engine performs abnormal operation, such as generation of large noise due to high injection pressure, when a learned value is calculated if the frequency of calculation of learned value or the frequency of correction is excessively high. The frequency of calculation of learned value or the frequency of correction can be properly determined according to the frequency of an ignition switch opening operation, the distance traveled by a vehicle or the secular reduction of injection quantity by changing the frequency of calculation of learned value or the frequency of correction according to the frequency of an ignition switch opening operation, the distance traveled by a vehicle or the secular reduction of injection quantity.
Reflecting the learned value stored by the learned value storage means is reflected in the calculation of injection quantities, set according to the operating condition of the engine and the fuel injection quantity, respectively for pilot injection, main injection, after injection and post injection. Thus, a proper fuel injection quantity (command injection quantity) can be determined by using a learned value as a correction corresponding to the deterioration of the performance of the injector due to the large amount of scatter of actual injection quantities with respect to the command injection pulse time for the injector even in a state where the engine is in operation at a high injection pressure and at a very small injection quantity in the range of, for example, 1 to 5 mm3/st, which is very difficult to guarantee even by a single injector.